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Evidence for replicative repair of DNA double-strand breaks leading to oncogenic translocation and gene amplification.

Difilippantonio MJ, Petersen S, Chen HT, Johnson R, Jasin M, Kanaar R, Ried T, Nussenzweig A - J. Exp. Med. (2002)

Bottom Line: Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway.Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture.Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. difilipm@mail.nih.gov

ABSTRACT
Nonreciprocal translocations and gene amplifications are commonly found in human tumors. Although little is known about the mechanisms leading to such aberrations, tissue culture models predict that they can arise from DNA breakage, followed by cycles of chromatid fusion, asymmetric mitotic breakage, and replication. Mice deficient in both a nonhomologous end joining (NHEJ) DNA repair protein and the p53 tumor suppressor develop lymphomas at an early age harboring amplification of an IgH/c-myc fusion. Here we report that these chromosomal rearrangements are initiated by a recombination activating gene (RAG)-induced DNA cleavage. Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway. Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture. Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

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Stabilization of broken chromosomes via chromatid fusion or chromosome capping. (A) Sequences from chromosomes 1, 3, and 16 are commonly used to cap the derivative chromosome. The presence of DNA from chromosomes 12 or 15 was confirmed by FISH when the region was too small to be visualized with painting probes. (B) Left panel: copying of the IgH locus onto chromosome 15 leaves der(15)a without a telomere (red) and results in amplification of both IgH Cα (green) and c-myc (pink). Stabilization of this chromosome occurs by the copying of telomeric sequences from other chromosomes (middle panel: unidentified with chromosome 3 paint; right panel: chromosome 3). (C) Dicentric chromosome stained with DAPI (blue) and hybridized with probes containing the IgH Cα (red) and IgH Cμ (green) loci.
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fig2: Stabilization of broken chromosomes via chromatid fusion or chromosome capping. (A) Sequences from chromosomes 1, 3, and 16 are commonly used to cap the derivative chromosome. The presence of DNA from chromosomes 12 or 15 was confirmed by FISH when the region was too small to be visualized with painting probes. (B) Left panel: copying of the IgH locus onto chromosome 15 leaves der(15)a without a telomere (red) and results in amplification of both IgH Cα (green) and c-myc (pink). Stabilization of this chromosome occurs by the copying of telomeric sequences from other chromosomes (middle panel: unidentified with chromosome 3 paint; right panel: chromosome 3). (C) Dicentric chromosome stained with DAPI (blue) and hybridized with probes containing the IgH Cα (red) and IgH Cμ (green) loci.

Mentions: Hybridization with the 15T BAC implied that the telomeric region of chromosome 15 was capping not only the normal chromosome 15, as expected, but also the der(12)a. Additionally, while both chromosomes 15 in scenario B were presumably protected from degradation by chromosome 15 telomeric sequences, der(12)b was not (Fig. 1). To determine if der(15)a and der(12)b were indeed protected from degradation by telomere sequences and from which chromosomes these might be derived, we used FISH and SKY analysis, respectively. In tumors in which IgH Cα was copied to chromosome 15 (scenario A), additional material at the ends of der(15)a was often found to be derived from different chromosomes (Fig. 2 A). Moreover, there were frequently variations in the length and composition at the end of der(15)a in different metaphases from the same tumor (Fig. 2 B). In some metaphases, the end of der(15)a consisted of amplified copies of IgH Cα and c-myc (Fig. 1, and Fig. 2 B, left panel); in others there appeared to be a single chromosome that capped der (15)a (Fig. 2 A, and Fig. 2 B, middle and right panels); while in still others we found tandem amplification of material from chromosomes 12 and 16 (Fig. 2 A). Additionally, in tumor N10527 we observed cells containing a dicentric chromosome with amplification of the IgH and c-myc loci (Fig. 2 C). Despite these differences in chromatin content at the end of der(15)a, all of the metaphases retained the clonal der(12)a containing 15T sequences (Fig. 2 B). The three tumors in scenario B also contained chromatin from chromosomes 1, 3 and/or 16 distal to the IgH Cα and c-myc genes (Fig. 2 A).


Evidence for replicative repair of DNA double-strand breaks leading to oncogenic translocation and gene amplification.

Difilippantonio MJ, Petersen S, Chen HT, Johnson R, Jasin M, Kanaar R, Ried T, Nussenzweig A - J. Exp. Med. (2002)

Stabilization of broken chromosomes via chromatid fusion or chromosome capping. (A) Sequences from chromosomes 1, 3, and 16 are commonly used to cap the derivative chromosome. The presence of DNA from chromosomes 12 or 15 was confirmed by FISH when the region was too small to be visualized with painting probes. (B) Left panel: copying of the IgH locus onto chromosome 15 leaves der(15)a without a telomere (red) and results in amplification of both IgH Cα (green) and c-myc (pink). Stabilization of this chromosome occurs by the copying of telomeric sequences from other chromosomes (middle panel: unidentified with chromosome 3 paint; right panel: chromosome 3). (C) Dicentric chromosome stained with DAPI (blue) and hybridized with probes containing the IgH Cα (red) and IgH Cμ (green) loci.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2196056&req=5

fig2: Stabilization of broken chromosomes via chromatid fusion or chromosome capping. (A) Sequences from chromosomes 1, 3, and 16 are commonly used to cap the derivative chromosome. The presence of DNA from chromosomes 12 or 15 was confirmed by FISH when the region was too small to be visualized with painting probes. (B) Left panel: copying of the IgH locus onto chromosome 15 leaves der(15)a without a telomere (red) and results in amplification of both IgH Cα (green) and c-myc (pink). Stabilization of this chromosome occurs by the copying of telomeric sequences from other chromosomes (middle panel: unidentified with chromosome 3 paint; right panel: chromosome 3). (C) Dicentric chromosome stained with DAPI (blue) and hybridized with probes containing the IgH Cα (red) and IgH Cμ (green) loci.
Mentions: Hybridization with the 15T BAC implied that the telomeric region of chromosome 15 was capping not only the normal chromosome 15, as expected, but also the der(12)a. Additionally, while both chromosomes 15 in scenario B were presumably protected from degradation by chromosome 15 telomeric sequences, der(12)b was not (Fig. 1). To determine if der(15)a and der(12)b were indeed protected from degradation by telomere sequences and from which chromosomes these might be derived, we used FISH and SKY analysis, respectively. In tumors in which IgH Cα was copied to chromosome 15 (scenario A), additional material at the ends of der(15)a was often found to be derived from different chromosomes (Fig. 2 A). Moreover, there were frequently variations in the length and composition at the end of der(15)a in different metaphases from the same tumor (Fig. 2 B). In some metaphases, the end of der(15)a consisted of amplified copies of IgH Cα and c-myc (Fig. 1, and Fig. 2 B, left panel); in others there appeared to be a single chromosome that capped der (15)a (Fig. 2 A, and Fig. 2 B, middle and right panels); while in still others we found tandem amplification of material from chromosomes 12 and 16 (Fig. 2 A). Additionally, in tumor N10527 we observed cells containing a dicentric chromosome with amplification of the IgH and c-myc loci (Fig. 2 C). Despite these differences in chromatin content at the end of der(15)a, all of the metaphases retained the clonal der(12)a containing 15T sequences (Fig. 2 B). The three tumors in scenario B also contained chromatin from chromosomes 1, 3 and/or 16 distal to the IgH Cα and c-myc genes (Fig. 2 A).

Bottom Line: Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway.Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture.Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

View Article: PubMed Central - PubMed

Affiliation: Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA. difilipm@mail.nih.gov

ABSTRACT
Nonreciprocal translocations and gene amplifications are commonly found in human tumors. Although little is known about the mechanisms leading to such aberrations, tissue culture models predict that they can arise from DNA breakage, followed by cycles of chromatid fusion, asymmetric mitotic breakage, and replication. Mice deficient in both a nonhomologous end joining (NHEJ) DNA repair protein and the p53 tumor suppressor develop lymphomas at an early age harboring amplification of an IgH/c-myc fusion. Here we report that these chromosomal rearrangements are initiated by a recombination activating gene (RAG)-induced DNA cleavage. Subsequent DNA repair events juxtaposing IgH and c-myc are mediated by a break-induced replication pathway. Cycles of breakage-fusion-bridge result in amplification of IgH/c-myc while chromosome stabilization occurs through telomere capture. Thus, mice deficient in NHEJ provide excellent models to study the etiology of unbalanced translocations and amplification events during tumorigenesis.

Show MeSH
Related in: MedlinePlus